There are many different kinds of icing and buttercream, so which are best for piping? Piping can be done with most any icing, but I prefer to use royal icing if I am piping on fondant and Swiss meringue buttercream if I am piping on buttercream. Royal icing goes hard and tends not to bleed into fondant, making for a nice clean look that cannot be wiped away easily. Buttercream, however, is a different story.
I like to keep my buttercream cakes in the refrigerator as long as possible. When using Swiss meringue buttercream or any type of buttercream that includes only butter and no shortening, the buttercream will harden on the cake when chilled, making it easier to work with when piping and more smudge resistant. Royal icing should not go into the fridge once it’s on a cake because the humidity will break down the royal icing, causing it to melt.
You will know your icing consistency is correct when you can pipe a string between your fingers and give it a little shake and it doesn’t break immediately. If it breaks quickly, your icing is too wet (add a little powdered sugar). If it is really hard to get out of the bag, your icing is too dry (add a little water).
Let’s begin with straight lines. It is best to practice guiding the icing rather than forcing the icing to go where you want it to go. When doing most piping work, try to keep the tip off of the cake or the practice mat. Let gravity do its job, while guiding the string of icing in the direction you want it to go.
Another way I like to practice is on a goblet or a flat bottle. It is great to practice on a mat, but most cake decorating is on the side of a cake that is usually upright and round, and that can make a big difference in your piping skills. Just because you are a whiz at swoops on the table does not mean you will be great at them on a real cake. So, practicing on a glass can give you a sense of decorating on a cake without the commitment and time involved in making and prepping a real cake.
If you make a mistake, or you end up with peaks of icing rather than nice dots, use a damp paintbrush and touch it gently to the royal icing to help it form into a small ball.
https://www.craftsy.com/cake-decorating/article/piping-techniques/
For me personally, THE MOST important thing is the royal icing consistency. Too thick, you are risking your hand cramping up. Icing that is too thin, icing won't hold its shape.
Icing should be about toothpaste consistency, or little thicker so to it holds the shape better but is easy to push out.
http://www.hanielas.com/2013/09/practicing-piping-with-royal-icing.html
Piping ideas and templates
https://www.pinterest.co.uk/zoemeganl/patisserie/piping/